Usnea barbata extract prevents ultraviolet-B induced prostaglandin E2 synthesis and COX-2 expression in HaCaT keratinocytes

Usnea barbata and its major constituent usnic acid are potent antimicrobial agents. Here, we have investigated anti-inflammatory properties of an U. barbata extract (UBE) containing 4% usnic acid in an ultraviolet-B (UVB) model with HaCaT keratinocytes. UVB irradiation induced PGE2 production and COX-2 expression in a time and dose-dependent manner. UBE inhibited PGE2 production at a half-maximal concentration of 60 μg/ml (2.4 μg/ml usnic acid) that did not affect the UVB-induced upregulation of COX-2, suggesting an effect on enzyme activity rather than on protein expression. The inhibition of PGE2 production by UBE was not due to cytotoxicity. Besides its known antimicrobial properties, UBE displays specific UVB protective effects that might be useful in the topical treatment of UVB-mediated inflammatory skin conditions.